Zusammenfassung: | |
The primary function of plant mitochondria is respiration, which is why they are often referred to as
“powerhouses of the cell”. Besides their central role in energy metabolism, plant mitochondria are
also involved in the photorespiratory C2 cycle and in the provision of carbon skeletons to support
efficient nitrogen assimilation. All these functions are catalyzed by mitochondrial proteins. Their
composition, abundance and interactions in plant mitochondria are the subject of this thesis. In yeast,
Trypanosomes, and several mammalian cell types, mitochondria are organized as extensive
mitochondrial networks, resulting in a situation where a cell only hosts few but large mitochondria. In
plants, hundreds of small mitochondria are only connected by fusion and fission over time but not
physically. Hence, the organelles form individual, functional units. Paradoxically, their biochemical and
physiological characterization focuses on large organelle populations and thereby disregards the
properties of the individual mitochondrion. This partially is based on the fact that cell biological
approaches capturing structural features of plant mitochondria often are of limited value for
understanding their physiological properties. Chapter 2.1 of this thesis models the protein content of
a single mitochondrion by combining proteomics with classical cell biology. Besides other insights into
the function of a single plant mitochondrion, it could be shown that proteins involved in ATP synthesis
and transport make up nearly half of the plant mitochondrial proteome. The five protein complexes of
the OXPHOS system contribute most to this segment of the mitochondrial proteome, underlining the
overall importance of mitochondrial ATP synthesis for the entire plant cell. Despite the central function
of OXHPOS components in plants, certain unicellular parasites and yeasts apparently do not need a
complete OXPHOS system. Intriguingly, it recently has been reported that the mitochondrial genome
of the multicellular parasitic flowering plant Viscum album (European mistletoe) is reduced and lacks
the genes encoding the mitochondrially encoded subunits of complex I. This implies that the
corresponding genes either have been lost or, alternatively, were transferred to the nuclear genome.
The consequences for the mitochondrial respiratory chain were so far unknown. Chapter 2.2 presents
data suggesting that V. album indeed lacks mitochondrial complex I. The absence of complex I is
accompanied by a rearrangement of the respiratory chain including (i) stable supercomplexes
composed of complexes III2 and IV, and (ii) the occurrence of numerous alternative oxidoreductases.
Mitochondria of V. album also possess less cristae than mitochondria from non-parasitic plants, which
can be explained by low amounts of ATP synthase dimers. The mitochondrial proteome consists of
proteins encoded in the nucleus or in the rudimentary mitochondrial genome. The few proteins
encoded on the mitochondrial genome are translated by mitochondrial ribosomes. While structure
and composition of these mitoribosomes are well established in yeast and mammals, the current
knowledge of plant mitoribosomes is negligible. Isolation of plant mitoribosomes is difficult due to
their sedimentation coefficient, which is very close to that of cytosolic ribosomes, their interaction
with the inner mitochondrial membrane, and the attachment of cytosolic ribosomes to the
mitochondrial surface. As part of this dissertation, plant mitoribosomes were analyzed via a novel
complexome profiling strategy (chapter 2.3). This revealed an unconventional molecular mass of the
small ribosomal subunit of plants. In addition, several pentatricopeptide repeat (PPR) proteins were
discovered to form part of both, the large and the small mitoribosomal subunit.
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Publikationstyp: | DoctoralThesis |
Publikationsstatus: | publishedVersion |
Erstveröffentlichung: | 2019 |
Schlagwörter (deutsch): | Pflanzliche Mitochondrien, Proteomik, Proteinkomplexe |
Schlagwörter (englisch): | Plant mitochondria, proteomics, protein complexes |
Fachliche Zuordnung (DDC): | 570 | Biowissenschaften, Biologie |